Abstract: This paper addresses a development of the decentralized robust control strategy fora reactor-regenerator system in fluidized catalytic cracking unit (FCCU).The problemunder study is to find a decentralized robust controller which could provide satisfied dynamic behaviors as the disturbances occurrence with unknown process dynamics.The resulting decentralized control algorithm could be obtained and performed through the measured process steady state gain matrix associated with some simple"on-line turning"procedures.As a result,the control configuration as given by Davison〔7〕is then improved.Finally,the proposed techniques have been successfully applied to a large production scale FCCU.The industrial application results show that the resulting systemgives satisfactory robustness and dynamic behavior,for instance,the variance and themaximal deviation of the reactor temperature are significantly reduced from 1.9℃ and 9.7℃ to 0.91℃ and 4.0℃ respectively.